U.S. patent application number 13/298582 was filed with the patent office on 2012-05-17 for method for producing photovoltaic cell.
This patent application is currently assigned to HITACHI CHEMICAL COMPANY, LTD.. Invention is credited to Shuuichirou Adachi, Mitsunori Iwamuro, Keiko Kizawa, Youichi Machii, Takeshi Nojiri, Kaoru Okaniwa, Akihiro Orita, Tetsuya Satou, Masato Yoshida.
Application Number | 20120122265 13/298582 |
Document ID | / |
Family ID | 46048145 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120122265 |
Kind Code |
A1 |
Machii; Youichi ; et
al. |
May 17, 2012 |
METHOD FOR PRODUCING PHOTOVOLTAIC CELL
Abstract
The method for producing a photovoltaic cell includes applying
an n-type diffusion layer forming composition including an n-type
impurity-containing glass powder and a dispersion medium onto a
first region on one surface side of a semiconductor substrate;
applying a p-type diffusion layer forming composition including a
p-type impurity-containing glass powder and a dispersion medium
onto a second region other than the first region on the surface of
the semiconductor substrate where the first region is provided; a
thermal diffusion process in which an n-type diffusion layer and a
p-type diffusion layer are formed by heat-treating the
semiconductor substrate onto which the n-type diffusion layer
forming composition and the p-type diffusion layer forming
composition are applied; and forming an electrode on each of the
first region where the n-type diffusion layer is formed and the
second region where the p-type diffusion layer is formed,
respectively.
Inventors: |
Machii; Youichi;
(Tsukuba-shi, JP) ; Yoshida; Masato; (Tsukuba-shi,
JP) ; Nojiri; Takeshi; (Tsukuba-shi, JP) ;
Okaniwa; Kaoru; (Tsukuba-shi, JP) ; Iwamuro;
Mitsunori; (Tsukuba-shi, JP) ; Adachi;
Shuuichirou; (Tsukuba-shi, JP) ; Orita; Akihiro;
(Tsukuba-shi, JP) ; Satou; Tetsuya; (Tsukuba-shi,
JP) ; Kizawa; Keiko; (Tsukuba-shi, JP) |
Assignee: |
HITACHI CHEMICAL COMPANY,
LTD.
|
Family ID: |
46048145 |
Appl. No.: |
13/298582 |
Filed: |
November 17, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61414578 |
Nov 17, 2010 |
|
|
|
Current U.S.
Class: |
438/69 ;
257/E31.127 |
Current CPC
Class: |
H01L 31/18 20130101;
Y02E 10/50 20130101; H01L 31/022441 20130101 |
Class at
Publication: |
438/69 ;
257/E31.127 |
International
Class: |
H01L 31/0232 20060101
H01L031/0232 |
Claims
1. A method for producing a photovoltaic cell, comprising:
applying, on a first region on one surface side of a semiconductor
substrate, an n-type diffusion layer forming composition including
an n-type impurity-containing glass powder and a dispersion medium;
applying, on a second region other than the first region on the
surface of the semiconductor substrate where the first region is
provided, a p-type diffusion layer forming composition including a
p-type impurity-containing glass powder and a dispersion medium; a
thermal diffusion process in which an n-type diffusion layer and a
p-type diffusion layer are formed by heat-treating the
semiconductor substrate onto which the n-type diffusion layer
forming composition and the p-type diffusion layer forming
composition are applied; and forming an electrode in the first
region where the n-type diffusion layer is formed and in the second
region where the p-type diffusion layer is formed,
respectively.
2. A method for producing a photovoltaic cell, comprising:
applying, on a first region on one surface side of a semiconductor
substrate, an n-type diffusion layer forming composition including
an n-type impurity-containing glass powder and a dispersion medium;
applying, on a second region other than the first region on the
surface of the semiconductor substrate where the first region is
provided, a p-type diffusion layer forming composition including a
p-type impurity-containing glass powder and a dispersion medium; a
thermal diffusion process in which an n-type diffusion layer and a
p-type diffusion layer are formed by heat-treating the
semiconductor substrate onto which the n-type diffusion layer
forming composition and the p-type diffusion layer forming
composition are applied; providing a protective layer in at least
one region selected from the first region, the second region, or a
third region other than the first and second regions on the surface
of the semiconductor substrate where the first and second regions
are formed, before the thermal diffusion process; and forming an
electrode in the first region where the n-type diffusion layer is
formed and in the second region where the p-type diffusion layer is
formed, respectively.
3. The method for producing a photovoltaic cell according to claim
2, wherein an oxide film is provided as a protective layer.
4. The method for producing a photovoltaic cell according to claim
1, wherein the n-type impurity includes at least one kind of
element selected from the group consisting of P (phosphorus) and Sb
(antimony).
5. The method for producing a photovoltaic cell according to claim
2, wherein the n-type impurity includes at least one kind of
element selected from the group consisting of P (phosphorus) and Sb
(antimony).
6. The method for producing a photovoltaic cell according to claim
1, wherein the p-type impurity includes at least one kind of
element selected from the group consisting of B (boron), Al
(aluminum), and Ga (gallium).
7. The method for producing a photovoltaic cell according to claim
2, wherein the p-type impurity includes at least one kind of
element selected from the group consisting of B (boron), Al
(aluminum), and Ga (gallium).
8. The method for manufacturing a photovoltaic cell according to
claim 1, wherein the n-type impurity-containing glass powder
includes, at least one kind of n-type impurity-containing material
selected from the group consisting of P.sub.2O.sub.3,
P.sub.2O.sub.5, and Sb.sub.2O.sub.3, and at least one kind of glass
component material selected from the group consisting of SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2, TiO.sub.2, and MoO.sub.3.
9. The method for manufacturing a photovoltaic cell according to
claim 2, wherein the n-type impurity-containing glass powder
includes, at least one kind of n-type impurity-containing material
selected from the group consisting of P.sub.2O.sub.3,
P.sub.2O.sub.5, and Sb.sub.2O.sub.3, and at least one kind of glass
component material selected from the group consisting of SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2, TiO.sub.2, and MoO.sub.3.
10. The method for producing a photovoltaic cell according to claim
1, wherein the p-type impurity-containing glass powder includes, at
least one kind of p-type impurity-containing material selected from
the group consisting of B.sub.2O.sub.3, Al.sub.2O.sub.3, and
Ga.sub.2O.sub.3, and at least one kind of glass component material
selected from the group consisting of SiO.sub.2, K.sub.2O,
Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO,
V.sub.2O.sub.5, SnO, ZrO.sub.2, TiO.sub.2, and MoO.sub.3.
11. The method for producing a photovoltaic cell according to claim
2, wherein the p-type impurity-containing glass powder includes, at
least one kind of p-type impurity-containing material selected from
the group consisting of B.sub.2O.sub.3, Al.sub.2O.sub.3, and
Ga.sub.2O.sub.3, and at least one kind of glass component material
selected from the group consisting of SiO.sub.2, K.sub.2O,
Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO,
V.sub.2O.sub.5, SnO, ZrO.sub.2, TiO.sub.2, and MoO.sub.3.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. 119(e) to
Provisional U.S. Patent Applications No. 61/414,578, filed Nov. 17,
2010, the disclosure of which is incorporated by reference
herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for producing a
photovoltaic cell.
[0004] 2. Description of the Related Art
[0005] A double-sided electrode type photovoltaic cell in which an
n-electrode is formed on a light receiving surface of a silicon
substrate and a p-electrode is formed on a rear surface of the
silicon substrate accounts for the majority of currently produced
photovoltaic cells. However, in regard to the double-sided
electrode type photovoltaic cell, solar light is not incident to
the silicon substrate directly under an n-electrode that is formed
on the light receiving surface, such that a current is not
generated at that portion.
[0006] Therefore, a rear surface electrode type photovoltaic cell
in which an electrode is not provided in a light receiving surface
of a photovoltaic cell, and both of the n-electrode and the
p-electrode are provided on a rear surface that is opposite to the
light receiving surface is suggested. In such a rear surface
electrode type photovoltaic cell, the incidence of the solar light
is not obstructed by an electrode formed on the light receiving
surface, such that a high conversion efficiency may be expected in
principle.
[0007] As a method of manufacturing the rear surface electrode type
photovoltaic cell, for example, the following manufacturing method
is known (For example, refer to Specification of U.S. Pat. No.
4,927,770).
[0008] First, a diffusion control mask is formed as a mask on the
entirety of the light receiving surface and the rear surface of the
silicon substrate. Here, the diffusion control mask has a function
of suppressing impurities from diffusing into a silicon
substrate.
[0009] Next, a part of the diffusion control mask on the rear
surface of the silicon substrate is removed to form an opening
portion.
[0010] In addition, when a p-type impurity is made to diffuse into
the rear surface of the silicon substrate from the opening portion
of the diffusion control mask, a p-type impurity diffusion layer is
formed only at the opening portion.
[0011] Next, after the entirety of the diffusion control mask on
the rear surface of the silicon substrate is removed, a diffusion
control mask is formed again on the rear surface of the silicon
substrate. Then, a part of the diffusion control mask on the rear
surface of the silicon substrate is removed, and an n-type impurity
is made to diffuse into the rear surface of the silicon substrate
from the opening portion. Accordingly, an n-type impurity layer is
formed.
[0012] Subsequently, when the entirety of the diffusion control
mask on the rear surface of the silicon substrate is removed, a
p-type impurity diffusion layer and an n-type impurity diffusion
layer are formed on the rear surface. Furthermore, a texture
structure, an antireflective film, a passivation film, electrodes,
or the like are formed, and thereby the rear surface electrode type
photovoltaic cell is obtained.
[0013] In addition, a method of manufacturing the rear surface
electrode type photovoltaic cell using a diffusing agent including
an n-type impurity and a diffusing agent including a p-type
impurity is disclosed (for example, refer to Japanese Patent
Application Laid-Open (JP-A) No. 2009-76546).
SUMMARY OF THE INVENTION
[0014] A first embodiment according to the present invention is a
method for producing a photovoltaic cell, including:
[0015] applying, on a first region on one surface side of a
semiconductor substrate, an n-type diffusion layer forming
composition including an n-type impurity-containing glass powder
and a dispersion medium;
[0016] applying, on a second region other than the first region on
the surface of the semiconductor substrate where the first region
is provided, a p-type diffusion layer forming composition including
a p-type impurity-containing glass powder and a dispersion
medium;
[0017] a thermal diffusion process in which an n-type diffusion
layer and a p-type diffusion layer are formed by heat-treating the
semiconductor substrate onto which the n-type diffusion layer
forming composition and the p-type diffusion layer forming
composition are applied; and
[0018] forming an electrode in the first region where the n-type
diffusion layer is formed and in the second region where the p-type
diffusion layer is formed, respectively.
[0019] A second embodiment of the present invention is a method for
producing a photovoltaic cell, including:
[0020] applying, on a first region on one surface side of a
semiconductor substrate, an n-type diffusion layer forming
composition including an n-type impurity-containing glass powder
and a dispersion medium;
[0021] applying, on a second region other than the first region on
the surface of the semiconductor substrate where the first region
is provided, a p-type diffusion layer forming composition including
a p-type impurity-containing glass powder and a dispersion medium;
a thermal diffusion process in which an n-type diffusion layer and
a p-type diffusion layer are formed by heat-treating the
semiconductor substrate onto which the n-type diffusion layer
forming composition and the p-type diffusion layer forming
composition are applied;
[0022] providing a protective layer in at least one region selected
from the first region, the second region, or a third region other
than the first and second regions on the surface of the
semiconductor substrate where the first and second regions are
formed, before the thermal diffusion process; and
[0023] forming an electrode in the first region where the n-type
diffusion layer is formed and in the second region where the p-type
diffusion layer is formed, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0024] In the manufacturing method disclosed in Specification of
U.S. Pate. No. 4,927,770, to form the p-type impurity diffusion
layer and the n-type impurity diffusion layer on the rear surface,
it is necessary to perform a complicated process, that is, to
repeatedly perform each process of the formation of the diffusion
control mask, the formation of the opening portion, the diffusion
of the impurities, and the removal of the diffusion control
mask.
[0025] In addition, in the manufacturing method disclosed in JP-A
No. 2009-76546, the processes of providing and removing the
protective layer are necessary, and in addition, the diffusion
layer may be formed in unnecessary places depending on the heat
treatment conditions at the time of the diffusion.
[0026] The present invention has been made in consideration of the
problems in the related art, and an object of the present invention
is to provide a method for producing a photovoltaic cell, in which,
in a process of producing a rear surface electrode type
photovoltaic cell, two different kinds of impurity diffusion layers
are able to be formed on the same surface by a simple process.
[0027] The invention includes the following embodiments.
[0028] <1> A method for producing a photovoltaic cell,
including: applying, on a first region on one surface side of a
semiconductor substrate, an n-type diffusion layer forming
composition including an n-type impurity-containing glass powder
and a dispersion medium; applying, on a second region other than
the first region on the surface of the semiconductor substrate
where the first region is provided, a p-type diffusion layer
forming composition including a p-type impurity-containing glass
powder and a dispersion medium; a thermal diffusion process in
which an n-type diffusion layer and a p-type diffusion layer are
formed by heat-treating the semiconductor substrate onto which the
n-type diffusion layer forming composition and the p-type diffusion
layer forming composition are applied; and forming an electrode in
the first region where the n-type diffusion layer is formed and in
the second region where the p-type diffusion layer is formed,
respectively.
[0029] <2> A method for producing a photovoltaic cell,
including: applying, on a first region on one surface side of a
semiconductor substrate, an n-type diffusion layer forming
composition including an n-type impurity-containing glass powder
and a dispersion medium; applying, on a second region other than
the first region on the surface of the semiconductor substrate
where the first region is provided, a p-type diffusion layer
forming composition including a p-type impurity-containing glass
powder and a dispersion medium; a thermal diffusion process in
which an n-type diffusion layer and a p-type diffusion layer are
formed by heat-treating the semiconductor substrate onto which the
n-type diffusion layer forming composition and the p-type diffusion
layer forming composition are applied; providing a protective layer
in at least one region selected from the first region, the second
region, or a third region other than the first and second regions
on the surface of the semiconductor substrate where the first and
second regions are formed, before the thermal diffusion process;
and forming an electrode in the first region where the n-type
diffusion layer is formed and in the second region where the p-type
diffusion layer is formed, respectively.
[0030] <3> The method for producing a photovoltaic cell
according to <2>, wherein an oxide film is provided as a
protective layer.
[0031] <4> The method for producing a photovoltaic cell
according to any one of <1> to <3>, wherein the n-type
impurity includes at least one kind of element selected from the
group consisting of P (phosphorus) and Sb (antimony).
[0032] <5> The method for producing a photovoltaic cell
according to any one of <1> to <4>, wherein the p-type
impurity includes at least one kind of element selected from the
group consisting of B (boron), Al (aluminum), and Ga (gallium).
[0033] <6> The method for manufacturing a photovoltaic cell
according to any one of <1> to <5>, wherein the n-type
impurity-containing glass powder includes, at least one kind of
n-type impurity-containing material selected from the group
consisting of P.sub.2O.sub.3, P.sub.2O.sub.5, and Sb.sub.2O.sub.3,
and at least one kind of glass component material selected from the
group consisting of SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO,
SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2,
TiO.sub.2, and MoO.sub.3.
[0034] <7> The method for producing a photovoltaic cell
according to any one of <1> to <6>, wherein the p-type
impurity-containing glass powder includes, at least one kind of
p-type impurity-containing material selected from the group
consisting of B.sub.2O.sub.3, Al.sub.2O.sub.3, and Ga.sub.2O.sub.3,
and at least one kind of glass component material selected from the
group consisting of SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO,
SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2,
TiO.sub.2, and MoO.sub.3.
[0035] In the present specification, the term "process" denotes not
only independent processes but also processes that cannot be
clearly distinguished from other processes as long as a purpose is
accomplished by the process. And "from . . . to . . . " denotes a
range including each of the minimum value and the maximum value of
the values described in this expression. Unless specifically
indicated, when an each ingredient of a composition includes plural
materials, a content of the each ingredient of the composition
denotes total amount of the plural materials including the
composition.
[0036] According to a first aspect of the invention, a method for
producing a photovoltaic cell includes a process of applying an
n-type diffusion layer forming composition including an n-type
impurity-containing glass powder and a dispersion medium on a first
region on one surface side of a semiconductor substrate; a process
of applying a p-type diffusion layer forming composition including
a p-type impurity-containing glass powder and a dispersion medium
on a second region other than the first region on the surface of
the semiconductor substrate where the first region is provided; a
thermal diffusion process in which an n-type diffusion layer and a
p-type diffusion layer are formed by heat-treating the
semiconductor substrate on which the n-type diffusion layer forming
composition and the p-type diffusion layer forming composition are
applied; a process of forming an electrode in each of the first
region where the n-type diffusion layer is formed and the second
region where the p-type diffusion layer is formed, respectively;
and optionally, other process as necessary.
[0037] The heat treatment is performed after the n-type diffusion
layer forming composition and the p-type diffusion layer forming
composition are applied to the first region and the second region,
respectively. Therefore, the n-type impurity diffuses into the
semiconductor substrate from the n-type diffusion layer forming
composition and thereby the n-type diffusion layer is formed in the
first region. In addition, the p-type impurity diffuses into the
semiconductor substrate from the p-type diffusion layer forming
composition, and thereby the p-type diffusion layer is formed in
the second region. The n-type diffusion layer and the p-type
diffusion layer are formed to have a desired shape with good
precision. In addition, it is possible to suppress the formation of
the n-type diffusion layer or the p-type diffusion layer in a third
region other than the first and second regions.
[0038] According to a second aspect of the present invention, a
method for producing a photovoltaic cell includes a process of
applying an n-type diffusion layer forming composition including an
n-type impurity-containing glass powder and a dispersion medium on
a first region on one surface side of a semiconductor substrate; a
process of applying a p-type diffusion layer forming composition
including a p-type impurity-containing glass powder and a
dispersion medium on a second region other than the first region on
the surface of the semiconductor substrate where the first region
is provided; a thermal diffusion process in which an n-type
diffusion layer and a p-type diffusion layer are formed by
heat-treating the semiconductor substrate on which the n-type
diffusion layer forming composition and the p-type diffusion layer
forming composition are applied; a process of providing a
protective layer in at least one region selected from the first
region, the second region, or a third region other than the first
and second regions on the surface of the semiconductor substrate
where the first and second regions are formed, before the thermal
diffusion process; a process of forming an electrode in the first
region where the n-type diffusion layer is formed and in the second
region where the p-type diffusion layer is formed, respectively;
and optionally, other processes as necessary.
[0039] When the protective layer is provided before the thermal
diffusion process, it is possible to more effectively suppress the
formation of the n-type diffusion layer or the p-type diffusion
layer in the third region other than the first and second
regions.
[0040] Hereinafter, the n-type diffusion layer forming composition
and the p-type diffusion layer forming composition of the present
invention will be described, and then the method for producing a
rear surface electrode type photovoltaic cell using the n-type
diffusion layer forming composition and the p-type diffusion layer
forming composition will be described.
[0041] n-Type Diffusion Layer Forming Composition
[0042] The n-type diffusion layer forming composition includes at
least one kind of an n-type impurity-containing glass powder, and
at least one kind of dispersion medium, and may optionally include
other additives in consideration of such things as the application
properties.
[0043] Here, the n-type diffusion layer forming composition
represents a material that includes an n-type impurity and that is
able to form an n-type diffusion layer through an application onto
a silicon substrate and a thermal diffusion of the n-type impurity.
When the n-type diffusion layer forming composition is used, the
n-type diffusion layer is formed at a desired portion.
[0044] n-Type Impurity-containing Glass Powder
[0045] The term "n-type impurity" included in the glass powder
refers to an element which is capable of forming an n-type
diffusion layer by doping thereof on a silicon substrate. As the
n-type impurity, elements of Group XV of the periodic table can be
used. Examples of the n-type impurity include P (phosphorous), Sb
(antimony), Bi (bismuth), and As (arsenic). From the viewpoint of
safety, convenience of vitrification or the like, P or Sb is
preferable.
[0046] Examples of the n-type impurity-containing material which is
used for introducing the n-type impurity into the glass powder
include P.sub.2O.sub.3, P.sub.2O.sub.5, Sb.sub.2O.sub.3,
Bi.sub.2O.sub.3, and As.sub.2O.sub.3. At least one selected from
P.sub.2O.sub.3, P.sub.2O.sub.5 and Sb.sub.2O.sub.3 is preferably
used.
[0047] Further, the melting temperature, softening point,
glass-transition point, chemical durability or the like of the
glass powder can be controlled by adjusting the component ratio, if
necessary. Further, the glass powder preferably contains the
components mentioned below.
[0048] Examples of the glass component material include SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2, WO.sub.3, MoO.sub.3, MnO,
La.sub.2O.sub.3, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, Y.sub.2O.sub.3,
TiO.sub.2, ZrO.sub.2, GeO.sub.2, TeO.sub.2, and Lu.sub.2O.sub.3. At
least one selected from SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O,
BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5, SnO,
ZrO.sub.2, TiO.sub.2 and MoO.sub.3 is preferably used.
[0049] Specific examples of the n-type impurity-containing glass
powder include materials including both the n-type
impurity-containing material and the glass component material, for
example, P.sub.2O.sub.5 based glass which includes P.sub.2O.sub.5
as the n-type impurity-containing material such as
P.sub.2O.sub.5--SiO.sub.2 (the n-type impurity-containing material
and the glass component material are listed in this order, and are
listed in the same order below)-based glass,
P.sub.2O.sub.5--K.sub.2O-based glass,
P.sub.2O.sub.5--Na.sub.2O-based glass,
P.sub.2O.sub.5--Li.sub.2O-based glass, P.sub.2O.sub.5--BaO-based
glass, P.sub.2O.sub.5--SrO-based glass, P.sub.2O.sub.5--CaO-based
glass, P.sub.2O.sub.5--MgO-based glass, P.sub.2O.sub.5--BeO-based
glass, P.sub.2O.sub.5--ZnO-based glass, P.sub.2O.sub.5--CdO-based
glass, P.sub.2O.sub.5--PbO-based glass,
P.sub.2O.sub.5--V.sub.2O.sub.5-based glass,
P.sub.2O.sub.5--SnO-based glass, P.sub.2O.sub.5--GeO.sub.2-based
glass, and P.sub.2O.sub.5--TeO.sub.2-based glass; Sb.sub.2O.sub.3
based glass in which P.sub.2O.sub.5 is replaced by Sb.sub.2O.sub.3
as an n-type impurity-containing material in the P.sub.2O.sub.5
based glass.
[0050] The n-type impurity-containing glass powder may include two
or more n-type impurity-containing materials such as
P.sub.2O.sub.5--Sb.sub.2O.sub.3, P.sub.2O.sub.5--As.sub.2O.sub.3 or
the like.
[0051] Although composite glass containing two components has been
exemplified in the above, glass powder containing three or more
components, such as P.sub.2O.sub.5--SiO.sub.2--V.sub.2O.sub.5 or
P.sub.2O.sub.5--SiO.sub.2--CaO, may also be used as necessary.
[0052] The content of the glass component material in the n-type
impurity-containing glass powder is preferably appropriately set
taking into consideration the melting temperature, the softening
point, the glass-transition point, and chemical durability.
Generally, the content of the glass component material is
preferably from 0.1% by mass to 95% by mass, and more preferably
from 0.5% by mass to 90% by mass.
[0053] Specifically, in case of
P.sub.2O.sub.5--SiO.sub.2--CaO-based glass, the content of CaO is
preferably from 1% by mass to 30% by mass, and more preferably from
5% by mass to 20% by mass.
[0054] The softening point of the n-type impurity-containing glass
powder is preferably in the range of from 200.degree. C. to
1000.degree. C., and more preferably from 300.degree. C. to
900.degree. C., from the viewpoint of diffusivity during the
diffusion treatment, and dripping.
[0055] The shape of the glass powder includes a substantially
spherical shape, a flat shape, a block shape, a plate shape, a
scale-like shape, and the like. From the viewpoint of the coating
property and uniform dispersion property, it is preferably a
spherical shape, a flat shape, or a plate shape.
[0056] The average particle diameter of the glass powder is
preferably 100 .mu.m or less. When a glass powder having an average
particle diameter of 100 .mu.m or less is used, a smooth coated
film can be easily obtained. Further, the average particle diameter
of the glass powder is more preferably 50 .mu.m or less and further
preferably 10 .mu.m or less. The lower limit of the average
particle diameter is not particularly limited, and preferably 0.01
.mu.m or more.
[0057] The average particle diameter of the glass powder means the
mean volume diameter, and may be measured by laser diffraction
particle size analyzer.
[0058] The n-type impurity-containing glass powder is prepared
according to the following procedure.
[0059] First, raw materials are weighed and placed in a crucible.
Examples of the material for the crucible include platinum,
platinum-rhodium, iridium, alumina, quartz and carbon, which are
appropriately selected taking into consideration the melting
temperature, atmosphere, reactivity with melted materials, and the
like.
[0060] Next, the raw materials are heated to a temperature
corresponding to the glass composition in an electric furnace,
thereby preparing a solution. At this time, stirring is preferably
applied such that the solution becomes homogenous.
[0061] Subsequently, the obtained solution is allowed to flow on a
zirconia substrate, a carbon substrate or the like to result in
vitrification of the solution.
[0062] Finally, the glass is pulverized into a powder. The
pulverization can be carried out by using a known method such as
using a jet mill, a bead mill, or a ball mill.
[0063] The content of the n-type impurity-containing glass powder
in the n-type diffusion layer forming composition is determined
taking into consideration coatability, diffusivity of n-type
impurities, and the like. Generally, the content of the glass
powder in the n-type diffusion layer forming composition is
preferably from 0.1% by mass to 95% by mass, more preferably from
1% by mass to 90% by mass, still more preferably from 1.5% by mass
to 85% by mass, and furthermore preferably from 2% by mass to 80%
by mass.
[0064] Dispersion Medium
[0065] Hereinafter, a dispersion medium will be described.
[0066] The dispersion medium is a medium which disperses the glass
powder in the composition. Specifically, a binder, a solvent or the
like is employed as the dispersion medium.
[0067] Binder
[0068] For example, the binder may be appropriately selected from a
polyvinyl alcohol, polyacrylamides, polyvinyl amides, polyvinyl
pyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide
alkyl sulfonic acid, cellulose derivatives such as cellulose
ethers, carboxymethylcellulose, hydroxyethylcellulose,
ethylcellulose, gelatin, starch and starch derivatives, sodium
alginates, xanthane and xanthane derivatives, guar and guar
derivatives, scleroglucan and scleroglucan derivatives, tragacanth
and tragacanth derivatives, dextrin and dextrin derivatives,
(meth)acrylic acid resins, (meth)acrylic acid ester resins (for
example, alkyl (meth)acrylate resins, dimethlaminoethyl
(meth)acrylate resins, or the like), butadiene resins, styrene
resins, and copolymers thereof, siloxane resins, and the like.
These compounds may be used individually or in a combination of two
or more thereof
[0069] The molecular weight of the binder is not particularly
limited and is preferably appropriately adjusted taking into
consideration the desired viscosity of the composition.
[0070] Solvent
[0071] Examples of the solvent include ketone solvents such as
acetone, methylethylketone, methyl-n-propylketone,
methyl-iso-propylketone, methyl-n-butylketone,
methyl-iso-butylketone, methyl-n-pentylketone,
methyl-n-hexylketone, diethylketone, dipropylketone,
di-iso-butylketone, trimethylnonanone, cyclohexanone,
cyclopentanone, methylcyclohexanone, 2,4-pentanedione, and
acetonylacetone; ether solvents such as diethyl ether, methyl ethyl
ether, n-di-n-propyl ether, di-iso-propyl ether, tetrahydrofuran,
methyl tetrahydrofuran, dioxane, dimethyl dioxane, ethylene glycol
dimethyl ether, ethylene glycol diethyl ether, ethylene glycol
di-n-propyl ether, ethylene glycol dibutyl ether, diethylene glycol
dimethyl ether, diethylene glycol diethyl ether, diethylene glycol
methyl ethyl ether, diethylene glycol methyl n-propyl ether,
diethylene glycol methyl n-butyl ether, diethylene glycol
di-n-propyl ether, diethylene glycol di-n-butyl ether, diethylene
glycol methyl n-hexyl ether, triethylene glycol dimethyl ether,
triethylene glycol diethyl ether, triethylene glycol methyl ethyl
ether, triethylene glycol methyl n-butyl ether, triethylene glycol
di-n-butyl ether, triethylene glycol methyl n-hexyl ether,
tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl
ether, tetradiethylene glycol methyl ethyl ether, tetraethylene
glycol methyl n-butyl ether, tetraethylene glycol di-n-butyl ether,
tetraethylene glycol methyl n-hexyl ether, tetraethylene glycol
di-n-butyl ether, propylene glycol dimethyl ether, propylene glycol
diethyl ether, propylene glycol di-n-propyl ether, propylene glycol
dibutyl ether, dipropylene glycol dimethyl ether, dipropylene
glycol diethyl ether, dipropylene glycol methyl ethyl ether,
dipropylene glycol methyl n-butyl ether, dipropylene glycol
di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene
glycol methyl n-hexyl ether, tripropylene glycol dimethyl ether,
tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl
ether, tripropylene glycol methyl n-butyl ether, tripropylene
glycol di-n-butyl ether, tripropylene glycol methyl n-hexyl ether,
tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl
ether, tetradipropylene glycol methyl ethyl ether, tetrapropylene
glycol methyl n-butyl ether, tetrapropylene glycol di-n-butyl
ether, tetrapropylene glycol methyl n-hexyl ether, and
tetrapropylene glycol di-n-butyl ether; ester solvents such as
methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate,
n-butyl acetate, i-butyl acetate, sec-butyl acetate, n-pentyl
acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methyl pentyl
acetate, 2-ethyl butyl acetate, 2-ethyl hexyl acetate,
2-(2-butoxyethoxy)ethyl acetate, benzyl acetate, cyclohexyl
acetate, methyl cyclohexyl acetate, nonyl acetate, methyl
acetoacetate, ethyl acetoacetate, glycol diacetate, methoxy
triglycol acetate, ethyl propionate, n-butyl propionate, i-amyl
propionate, diethyl oxalate, di-n-butyl oxalate, methyl lactate,
ethyl lactate, n-butyl lactate, n-amyl lactate,
.gamma.-butyrolactone, and .gamma.-valerolactone; ether acetate
solvents such as ethylene glycol methyl ether propionate, ethylene
glycol ethyl ether propionate, ethylene glycol methyl ether
acetate, ethylene glycol ethyl ether acetate, diethylene glycol
methyl ether acetate, diethylene glycol ethyl ether acetate,
diethylene glycol-n-butyl ether acetate, propylene glycol methyl
ether acetate, propylene glycol ethyl ether acetate, propylene
glycol propyl ether acetate, dipropylene glycol methyl ether
acetate, and dipropylene glycol ethyl ether acetate; aprotic polar
sovents such as acetonitrile, N-methyl pyrrolidinone, N-ethyl
pyrrolidinone, N-propyl pyrrolidinone, N-butyl pyrrolidinone,
N-hexyl pyrrolidinone, N-cyclohexyl pyrrolidinone, N,N-dimethyl
formamide, N,N-dimethyl acetamide, and dimethyl sulfoxide; alcohol
solvents such as methanol, ethanol, n-propanol, i-propanol,
n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol,
i-pentanol, 2-methylbutanol, sec-pentanol, t-pentanol, 3-methoxy
butanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol,
sec-heptanol, n-octanol, 2-ethylhexanol, sec-octanol, n-nonyl
alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol,
sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol,
cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol,
1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol,
dipropylene glycol, triethylene glycol, and tripropylene glycol;
glycol monoether solvents such as ethylene glycol monomethyl ether,
ethylene glycol monoethyl ether, ethylene glycol monophenyl ether,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol mono-n-butyl ether, diethylene glycol
mono-n-hexyl ether, ethoxy triglycol, tetraethylene glycol
mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene
glycol monomethyl ether, dipropylene glycol monoethyl ether, and
tripropylene glycol monomethyl ether; terpene solvents such as
.alpha.-terpinene, .alpha.-terpinenol, myrcene, allo-ocimene,
limonene, dipentene, .alpha.-dipentene, .beta.-dipentene,
terpinenol, carvone, ocimene, and phellandrene; water, and the
like. These solvents may be used individually or in a combination
of two or more thereof From the viewpoint of the coating property
of the composition for forming an n-type diffusion layer at a
substrate, .alpha.-terpinenol, diethylene glycol mono-n-butyl
ether, and diethylene glycol mono-n-butyl ether acetate is
preferable, and .alpha.-terpinenol and diethylene glycol
mono-n-butyl ether is more preferable.
[0072] The content of the dispersion medium in the n-type diffusion
layer forming composition is determined taking into consideration
coatability and n-type impurity concentration.
[0073] The viscosity of the n-type diffusion layer forming
composition is preferably from 10 mPas to 1,000,000 mPas, and more
preferably from 50 mPas to 500,000 mPas, from the viewpoint of
coatability.
[0074] p-Type Diffusion Layer Forming Composition
[0075] The p-type diffusion layer forming composition includes at
least one kind of p-type impurity-containing glass powder, and at
least one kind of dispersion medium, and may optionally include
other additives in consideration of the coating properties.
[0076] Here, the p-type diffusion layer forming composition
represents a material that includes a p-type impurity and that is
able to form a p-type diffusion layer through being applied onto a
silicon substrate and then thermally diffusing the p-type impurity.
When the p-type diffusion layer forming composition is used, the
p-type diffusion layer is formed at a desired portion.
[0077] Since a p-type impurity component in the glass powder is
hardly volatilized even during sintering, a p-type diffusion layer
is prevented from also being formed on the rear surface or side
face, rather than on the front surface alone due to the generation
of volatile gases. It is assumed that the reason for this is that
the p-type impurity component combines with an element in a glass
powder, or is absorbed into the glass, as a result of which the
p-type impurity component is hardly volatilized.
[0078] p-Type Impurity-containing Glass Powder
[0079] The term "p-type impurity" included in the glass powder
refers to an element which is capable of forming a p-type diffusion
layer by doping thereof on a silicon substrate. As the p-type
impurity, elements of Group XIII of the periodic table can be used.
Examples of the p-type impurity include B (boron), Al (aluminum),
and Ga (gallium).
[0080] Examples of the p-type impurity-containing material include
B.sub.2O.sub.3, Al.sub.2O.sub.3, and Ga.sub.2O.sub.3. At least one
selected from B.sub.2O.sub.3, Al.sub.2O.sub.3, and Ga.sub.2O.sub.3
is preferably used.
[0081] Further, the melting temperature, softening point,
glass-transition point, chemical durability or the like of the
glass powder can be controlled by adjusting the component ratio, if
necessary. Further, the glass powder preferably contains the
components mentioned below.
[0082] Examples of the glass component material include SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, Tl.sub.2O, V.sub.2O.sub.5, SnO, ZrO.sub.2, WO.sub.3,
MoO.sub.3, MnO, La.sub.2O.sub.3, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5,
Y.sub.2O.sub.3, TiO.sub.2, GeO.sub.2, TeO.sub.2, and
Lu.sub.2O.sub.3. At least one selected from SiO.sub.2, K.sub.2O,
Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO,
V.sub.2O.sub.5, SnO, ZrO.sub.2, TiO.sub.2 and MoO.sub.3 is
preferably used.
[0083] Specific examples of the p-type impurity-containing glass
powder include those including both the p-type impurity-containing
material and the glass component material such as, for example,
B.sub.2O.sub.3 based glass which includes B.sub.2O.sub.3 as the
p-type impurity such as B.sub.2O.sub.3--SiO.sub.2 (the p-type
impurity-containing material and the glass component material are
listed in this order, and are listed in the same order below) based
glass, B.sub.2O.sub.3--ZnO based glass, B.sub.2O.sub.3--PbO based
glass, single B.sub.2O.sub.3 based glass; Al.sub.2O.sub.3 based
glass which includes Al.sub.2O.sub.3 as the acceptor element such
as Al.sub.2O.sub.3--SiO.sub.2 based glass; and Ga.sub.2O.sub.3
based glass which includes Ga.sub.2O.sub.3 as the acceptor element
such as Ga.sub.2O.sub.3--SiO.sub.2 based glass.
[0084] The p-type impurity-containing glass powder may include two
or more p-type impurity-containing materials such as
Al.sub.2O.sub.3--B.sub.2O.sub.3, Ga.sub.2O.sub.3--B.sub.2O.sub.3 or
the like.
[0085] Although composite glasses containing one or two components
have been exemplified in the above, glass powder containing three
or more components, such as B.sub.2O.sub.3--SiO.sub.2--Na.sub.2O,
may also be used as necessary.
[0086] The content of the glass component material in the p-type
impurity-containing glass powder is preferably appropriately set
taking into consideration the melting temperature, the softening
point, the glass-transition point, and chemical durability.
Generally, the content of the glass component material is
preferably from 0.1% by mass to 95% by mass, and more preferably
from 0.5% by mass to 90% by mass.
[0087] The softening point of the p-type impurity-containing glass
powder is preferably in the range of from 200.degree. C. to
1000.degree. C., and more preferably from 300.degree. C. to
900.degree. C., from the viewpoint of diffusivity during the
diffusion treatment, and dripping.
[0088] The shape of the glass powder includes a substantially
spherical shape, a flat shape, a block shape, a plate shape, a
scale-like shape, and the like. From the viewpoint of coating
property and uniform dispersion property, it is preferably a
spherical shape, a flat shape, or a plate shape.
[0089] The average particle diameter of the glass powder is
preferably 100 .mu.m or less. When a glass powder having an average
particle diameter of 100 .mu.m or less is used, a smooth coated
film can be easily obtained. Further, the average particle diameter
of the glass powder is more preferably 50 .mu.m or less and further
preferably 10 .mu.m or less. The lower limit of the average
particle diameter is not particularly limited, and preferably 0.01
.mu.m or more.
[0090] The p-type impurity-containing glass powder is prepared
according to the same procedure described in the n-type
impurity-containing glass powder.
[0091] The content of the p-type impurity-containing glass powder
in the p-type diffusion layer forming composition is determined
taking into consideration coatability, diffusivity of n-type
impurities, and the like. Generally, the content of the glass
powder in the p-type diffusion layer forming composition is
preferably from 0.1% by mass to 95% by mass, more preferably from
1% by mass to 90% by mass, still more preferably from 1.5% by mass
to 85% by mass, and furthermore preferably from 2% by mass to 80%
by mass.
[0092] As the dispersion medium, the same material described in the
n-type diffusion layer forming composition may be used.
[0093] The content of the dispersion medium in the p-type diffusion
layer forming composition is determined taking into consideration
coatability and p-type impurity concentration.
[0094] The viscosity of the p-type diffusion layer forming
composition is preferably from 10 mPas to 1,000,000 mPas, and more
preferably from 50 mPas to 500,000 mPas, from the viewpoint of
coatability.
[0095] [Method for Producing Photovoltaic Cell]
[0096] First, a damage layer on the surface of the silicon
substrate is removed through etching using an acidic or alkalic
solution.
[0097] Next, a protective film formed of a silicon oxide film or a
silicon nitride film on one surface side of the silicon substrate
is formed. Here, the silicon oxide film may be formed, for example,
by a normal pressure CVD method using silane gas and oxygen. In
addition, the silicon nitride film may be formed, for example, by a
plasma CVD method using silane gas, ammonia gas, and nitrogen
gas.
[0098] Next, a minute concavo-convex structure called a texture
structure is formed on the surface of the side where the protective
film of the silicon substrate is not formed. The texture structure
may be formed, for example, by immersing the silicon substrate on
which the protective film is formed in liquid including potassium
hydroxide and isopropyl alcohol (IPA) at approximately 80.degree.
C.
[0099] Subsequently, the silicon substrate is immersed in a
hydrofluoric acid and thereby the protective film is etched and
removed.
[0100] The above described process of texture structure forming may
be performed after a diffusion layer described later is formed.
[0101] Next, the n-type diffusion layer and the p-type diffusion
layer are selectively formed in the first region and the second
region on the same plane of the silicon substrate,
respectively.
[0102] The shape and size of the first region and the second region
are not particularly limited, but may be appropriately selected
from the shape and size of the n-type diffusion layer and the
p-type diffusion layer that are commonly adopted in the rear
surface electrode type photovoltaic cell.
[0103] Specifically, for example, the n-type diffusion layer
forming composition is applied onto the first region on a surface
(hereinafter, referred to as "rear surface") that is opposite to
the surface serving as the light receiving surface of the silicon
substrate. The shape and size of the first region is appropriately
selected according to, for example, the shape and size of the
n-type diffusion layer that is formed. As the shape, for example, a
line shape may be exemplified. In addition, the line width may be,
for example, from 100 .mu.m to 300 .mu.m.
[0104] In addition, the p-type diffusion layer forming composition
is applied onto the second region on the rear surface of the
silicon substrate. The shape and size of the second region is
appropriately selected according to, for example, the shape and
size of the p-type diffusion layer that is formed. As the shape,
for example, a line shape may be exemplified. In addition, the line
width may be, for example, from 500 .mu.m to 900 .mu.m.
[0105] It is preferable that the first region and the second region
be provided with a predetermined interval without being brought
into contact with each other. The interval between the first region
and the second region may be appropriately selected according to
various physical properties of the n-type diffusion layer forming
composition and the p-type diffusion layer forming composition. For
example, the interval may be set to from 1 mm to 3 mm.
[0106] When the predetermined interval is provided in the first
region and the second region, it is possible to improve a power
generation efficiency of the rear surface electrode type
photovoltaic cell that is constructed.
[0107] In addition, the sequence of applying the n-type diffusion
layer forming composition and the p-type diffusion layer forming
composition is not particularly limited. That is, after the n-type
diffusion layer forming composition is applied onto the first
region, the p-type diffusion layer forming composition may be
applied onto the second region. In addition, after the p-type
diffusion layer forming composition is applied onto the second
region, the n-type diffusion layer forming composition may be
applied onto the first region. Furthermore, the n-type diffusion
layer forming composition and the p-type diffusion layer forming
composition may be applied at the same time depending on the
application method.
[0108] The method of applying the n-type diffusion layer forming
composition and the p-type diffusion layer forming composition is
not particularly limited, but a commonly used method may be used.
For example, a printing method such as a screen printing method and
a gravure printing method, a spinning method, a brush coating, a
spraying method, a doctor blade method, a roll coater method, an
ink jet method, or the like may be used. Furthermore, the method of
applying the n-type diffusion layer forming composition and the
p-type diffusion layer forming composition may be the same as each
other or be different from each other.
[0109] There is no particular limit to the application amount of
the n-type diffusion layer forming composition and the p-type
diffusion layer forming composition. For example, an amount of the
glass powder may be set to from 0.01 g/m.sup.2 to 100 g/m.sup.2,
and more preferably from 0.1 g/m.sup.2 to 10 g/m.sup.2. Here, the
application amount of n-type diffusion layer forming composition
and the application amount of p-type diffusion layer forming
composition may be independently and appropriately selected
according to the construction of the n-type diffusion layer forming
composition and the p-type diffusion layer forming composition, or
the impurity concentration in the n-type diffusion layer and the
p-type diffusion layer that are formed, respectively.
[0110] After the n-type diffusion layer forming composition and the
p-type diffusion layer forming composition are applied onto the
silicon substrate, a heating process of removing at least a part of
the dispersion medium may be provided. In the heating process, for
example, when a heating treatment is performed at from 100.degree.
C. to 200.degree. C., it is possible to volatilize at least part of
a solvent. In addition, for example, at least a part of a binder
may be removed through a heating treatment at from 200.degree. C.
to 500.degree. C.
[0111] The heating process may be performed after applying either
the n-type diffusion layer forming composition or the p-type
diffusion layer forming composition, or may be performed after
applying both of these compositions.
[0112] Next, when the silicon substrate onto which the n-type
diffusion layer forming composition and the p-type diffusion layer
forming composition are applied is heat-treated, the n-type
diffusion layer and the p-type diffusion layer are formed. Through
the heat treatment, the n-type impurity diffuses into the silicon
substrate from the n-type diffusion layer forming composition
applied onto the first region, and the p-type impurity diffuses
into the silicon substrate from the p-type diffusion layer forming
composition applied onto the second region, and thereby the n-type
diffusion layer and the p-type diffusion layer are formed.
[0113] In the present invention, the n-type diffusion layer forming
composition and p-type diffusion layer forming composition are
used, such that it is possible to form the n-type diffusion layer
and the p-type diffusion layer to have a desired shape with an
excellent precision. Furthermore, even when a protective layer
described later is not provided, it is possible to suppress the
formation of the n-type diffusion layer and the p-type diffusion
layer in a region where the diffusion is not necessary.
[0114] The temperature of the heat treatment is not particularly
limited as long as the n-type diffusion layer and the p-type
diffusion layer can be formed, but it is preferable that the
temperature be from 800.degree. C. to 1100.degree. C., more
preferably from 850.degree. C. to 1100.degree. C., and further more
preferably from 900.degree. C. to 1100.degree. C.
[0115] As described above, a glass layer remains on the silicon
substrate on which the n-type diffusion layer and the p-type
diffusion layer are formed, but it is preferable to remove the
glass layer. For the removal of the glass layer, a known method
such as a method of immersing the silicon substrate in an acid such
as a hydrofluoric acid, and a method of immersing the silicon
substrate in an alkali, such as sodium hydroxide, may be
exemplified.
[0116] In the present invention, before the heat treatment process
of forming the n-type diffusion layer and the p-type diffusion
layer, the protective layer may be formed in at least a part of the
rear surface of the silicon substrate. When the protective layer is
provided, it is possible to effectively suppress the formation of
the diffusion layer through a diffusion of the n-type impurity or
the p-type impurity into a region other than a desired region.
[0117] The protective layer may be formed on at least one region
selected from the first region, the second region, or a third
region other than the first and second regions on a rear surface of
the silicon substrate. That is, the protective layer is provided in
at least one of first region onto which the n-type diffusion layer
forming composition is applied and the second region onto which the
p-type diffusion layer forming composition is applied, and on the
third region, or the entirety of the rear surface.
[0118] Here, in a case where the protective layer is provided in
the third region, the protective layer may be provided before the
n-type diffusion layer forming composition or the p-type diffusion
layer forming composition is applied.
[0119] The protective layer is not particularly limited as long as
it has a function of suppressing the invasion of the n-type
impurity and the p-type impurity, which are scattered by the
heating treatment, into a region other than a desired region on the
silicon substrate, but it is preferable to use a silicon oxide.
Here, the silicon oxide film used as the protective layer may be
formed by applying a paste including a silicon compound, an organic
solvent, and a thickener through a spin coat, a screen printing
method, a gravure printing method, ink jet printing method, or the
like.
[0120] In addition, it is possible to form the protective layer
formed of a silicon oxide using silane gas and oxygen gas through
an atmospheric pressure CVD method.
[0121] It is preferable to remove the protective layer after the
heat treatment for forming the n-type diffusion layer and the
p-type diffusion layer. For example, in a case where the protective
layer is formed of a glass layer, for the removal of the protective
layer, a known method such as a method of immersing the substrate
in an acid such as a hydrofluoric acid, and a method of immersing
the substrate in an alkali such as sodium hydroxide may be
exemplified. In addition, at the time of removing the protective
layer, a glass layer derived from the n-type diffusion layer
forming composition and the p-type diffusion layer forming
composition may be removed at the same time.
[0122] After the n-type diffusion layer and the p-type diffusion
layer are formed, it is preferable to form a passivation film on
the silicon substrate at the rear surface side. Here, as the
passivation film, a silicon oxide film, a silicon nitride film, a
laminated film thereof, or the like may be used. The silicon oxide
film making up the passivation film may be formed through, for
example, a thermal oxidation method or an atmospheric pressure CVD
method, and the silicon nitride film making up the passivation film
may be formed through, for example, a plasma CVD method. In
addition, before the passivation film is formed, the rear surface
of the silicon substrate may be cleaned by a method that is well
known in the related art.
[0123] Next, it is preferable to form an antireflective film on a
surface of the silicon substrate at the side where a texture
structure is formed. Here, as the antireflective film, for example,
a nitride film formed through a plasma CVD method may be used.
[0124] Next, electrodes are formed on the n-type diffusion layer
and the p-type diffusion layer formed as described above,
respectively.
[0125] Specifically, for example, a part of the passivation film
formed on the rear surface is removed, and thereby a part of the
surface of the n-type diffusion layer and the p-type diffusion
layer is exposed, respectively. Here, for the removal of the
passivation film, a method that is well known in the related art
may be used.
[0126] In addition, when an n-electrode is formed on the surface of
the exposed n-type diffusion layer, and a p-electrode is formed on
the surface of the exposed p-type diffusion layer, a rear surface
electrode type photovoltaic cell is manufactured. The n-electrode
and the p-electrode may be formed by applying a silver-containing
electrode material onto the exposed surface of the n-type diffusion
layer and the p-type diffusion layer, respectively, and by drying
and/or baking the electrode material. In addition to this, the
n-electrode and the p-electrode may be formed through a vapor
deposition method.
[0127] In the present invention, the n-type impurity and the p-type
impurity are vitrified, such that it is possible to suppress the
diffusion of the n-type impurity and the p-type impurity into a
region in which the diffusion is unnecessary at the time of forming
the diffusion layer. Furthermore, the suppressing effect may be
further improved by forming a protective film.
EXAMPLES
[0128] Hereinafter, the present invention will be described in
detail with reference to examples, but the present invention is not
limited to the examples. In addition, if not particularly
mentioned, as chemicals, a reagent is used as a whole. In addition,
"part" and "%" are based on a mass.
Example 1
[0129] A glass powder whose particle shape is substantially
spherical, average particle diameter is 0.25 .mu.m and softening
point is about 800.degree. C. (including P.sub.2O.sub.5, SiO.sub.2,
and CaO as main components, in a content rate of 50%, 43%, and 7%,
respectively), ethyl cellulose, and terpineol are blended and made
into a paste in an amount of 10 g, 4 g, and 86 g, respectively, and
thereby the n-type diffusion layer forming composition was
prepared.
[0130] Subsequently, a glass powder whose particle shape is
substantially spherical, average particle diameter is 1.5 .mu.m and
softening point is about 810.degree. C. (including B.sub.2O.sub.3,
SiO.sub.2, CaO, MgO, BaO as main components, in a content of 30%,
40%, 10%, 10%, and 10%, respectively), ethyl cellulose, and
terpineol are blended and made into a paste in an amount of 20 g, 4
g, and 76 g, respectively, and thereby the p-type diffusion layer
forming composition was prepared.
[0131] The particle shape of the glass powder was judged by
observation with a scanning electron microscope (trade name:
TM-1000, manufactured by Hitachi High-Technologies Corporation).
The average diameter of the glass powder was calculated with a
laser diffraction particle size analyzer (measurement wave length:
632 nm, trade name: LS 13 320, manufactured by Beckman Coulter,
Inc.). The softening point of the glass powder was measured by a
differential thermal analysis (DTA) curve with a Thermo Gravimetry
Differential Thermal Analyzer (trade name: DTG-60H, manufactured by
SHIMADZU CORPORATION).
[0132] Next, the n-type diffusion layer forming composition was
applied in a line shape onto a surface of the silicon substrate
through screen printing, and the applied composition was dried at
150.degree. C. for 10 minutes. Subsequently, the p-type diffusion
layer forming composition was applied in a line shape onto the same
surface of the silicon substrate through a screen printing, with a
distance from the region where the n-type diffusion layer forming
composition was applied, and the applied composition was dried at
150.degree. C. for 10 minutes. Then, a binder removal treatment was
performed at 350.degree. C. for 3 minutes.
[0133] Next, a heat treatment was performed in an atmosphere at
950.degree. C. for 10 minutes, and thereby the n-type impurity and
the p-type impurity were made to diffuse into the silicon
substrate. Accordingly, the n-type diffusion layer and the p-type
diffusion layer were formed.
[0134] Subsequently, the glass layer remaining on the surface of
the silicon substrate was removed by a hydrofluoric acid.
[0135] Next, the diffusion state of the impurity of the silicon
substrate was confirmed through an SIMS measurement. Through the
measurement, it was confirmed that in a portion where the n-type
diffusion layer forming composition was applied, P (phosphorus)
diffused to a distance of approximately 0.7 .mu.m from the surface.
In addition, it was confirmed that in a portion where the p-type
diffusion layer forming composition was applied, B (boron) diffused
to a distance of approximately 0.6 .mu.m from the surface. On the
contrary, in a portion where the diffusion layer forming
composition was not applied, P (phosphorus) and B (boron) did not
diffuse.
[0136] The SIMS measurement was performed using an IMS-7F
manufactured by CAMECA SAS, in which O.sub.2.sup.+ and Cs.sup.+
were used as primary ions.
Example 2
[0137] In Example 1, the n-type diffusion layer and the p-type
diffusion layer were formed similarly to Example 1 except that
after the binder removal treatment, a silicon oxide film as a
protective film was formed on the entirety of the application
surface of the diffusion layer forming composition through an
atmospheric pressure CVD method with a thickness of 300 nm, and
then a heat treatment was performed in a nitrogen atmosphere.
Subsequently, the glass layer remaining on the surface of the
silicon substrate was removed by a hydrofluoric acid.
[0138] Next, as described above, the diffusion state of the
impurity of the silicon substrate was confirmed through an SIMS
measurement. Through the measurement, it was confirmed that in a
portion where the n-type diffusion layer forming composition was
applied, P (phosphorus) diffused to a distance of approximately 0.7
.mu.m from the surface. In addition, it was confirmed that in a
portion where the p-type diffusion layer forming composition was
applied, B (boron) diffused to a distance of approximately 0.6
.mu.m from the surface. On the contrary, in a portion where the
diffusion layer forming composition was not applied, P (phosphorus)
and B (boron) did not diffuse.
[Manufacturing Photovoltaic Cell]
[0139] Using the silicon substrate obtained as described above in
which the n-type diffusion layer and the p-type diffusion layer
were formed, an n-electrode was formed on the n-type diffusion
layer and the p-electrode was formed on the p-type diffusion layer,
respectively, through a normal method, and thereby a rear surface
electrode type photovoltaic cell was manufactured. The obtained
rear surface electrode type photovoltaic cell showed excellent
photo-conversion characteristics.
[0140] The foregoing description of the embodiments of the present
invention has been provided for the purposes of description. It is
not intended to be exhaustive or to limit the present invention to
the precise forms disclosed. Obviously, many modifications and
variations will be apparent to practitioners skilled in the art.
The embodiments were chosen and described in order to best explain
the principles of the present invention and its practical
applications, thereby enabling others skilled in the art to
understand the present invention for various embodiments and with
the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the present
invention be defined by the following claims and their
equivalents.
[0141] All publications, patent applications, and technical
standards mentioned in this specification are herein incorporated
by reference to the same extent as if each individual publication,
patent application, or technical standard was specifically and
individually indicated to be incorporated by reference.
* * * * *